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SubjectRe: ide-cd problems
On Fri, Aug 06 2004, Alan Cox wrote:
> On Gwe, 2004-08-06 at 07:23, Jens Axboe wrote:
> > Perhaps if you acknowledge that it wont be perfect, then it's becomes
> > more acceptable imo. So you can issue some commands that do write to the
> > drive even as a regular user, but none that permanently alter the state
> > of the drive or its media (to the best of our knowledge). Other commands
> > you let through.
>
> The code you included is roughly the kind of filtering I mean except
> that unknown commands must not get through without CAP_SYS_RAWIO.
> Anything that is doubtful doesn't get through. As to the location you do
> it there are at least two ways to handle that. One is that you stick the
> CAP_SYS_RAWIO of the requester in a flag in the request block the other
> is that you do it at the top layer. Some BSD socket implementations take
> the former approach and it works very well as the driver can make a
> final decision but is told the rights attached to the command.
>
> So once its
>
> switch()
> {
> case READ6:
> case READ10:
> ...
> /* Always */
> break;
> case WRITE6:
> case WRITE10:
> ...
> /* if write */
> default:
> if(capable(CAP_SYS_RAWIO))
> /* Only administrators get to do arbitary things */
>
> I agree with it.

That's the case I don't agree with, and why I didn't like the idea
originally. That suddenly requires a patching of the kernel because of
new commands in new devices. Like when dvd readers became common, you
can't just require people to update their kernel because a few new
commands are needed to drive them from user space.

--
Jens Axboe

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